1) Field of the Invention
The present invention relates to a technology to create an image processing program for decrypting and expanding moving image data to output a moving image to a display.
2) Description of the Related Art
In recent years, due to development of information digitalizing techniques and spread of the Internet (particularly, high-speed broadband Internet), various kinds of copyrighted works protected by copyright law are digitalized and widely distributed via recording medium, such as a compact disk-read only memory (CD-ROM) or a digital versatile disk (DVD), and transmission medium such as the Internet, cable television (CATV), or satellite broadcasting.
One of the unavoidable problems with the digitalized information is illegal copying of the information without getting permission from the copyright holders. Since the digitalized information is not deteriorated by copying, when the illegal copying is carried out beyond a legal scope (for example, file exchange on the Internet), the copyrights and the right of use of the information are considerably infringed.
While this problem is quite noticeable in music industry, which causes a decrease in sales of music CDs, illegal copying of moving images (movies) is also predicted to escalate hereafter.
FIG. 1 is a block diagram of a conventional image processing apparatus. Moving images distributed via, for example, the Internet are encrypted by predetermined encryption keys to prevent unauthorized people from snooping the moving images while transmission, and compressed by a predetermined method such as motion pictures expert group (MPEG) format to reduce a data size. A program to decrypt and expand the moving image data (hereinafter, “image processing program”) is pre-installed in the image processing apparatus.
The moving images transmitted from network interface card (NIC) 100 via a peripheral component interconnect (PCI) bus 101 are temporarily stored in a hard disc drive (HDD) 102, and are read by a processor 103 into a main memory 104 according to an operation by a user such as pressing a “play button”.
A processor 103 that executes the image processing program also read into the main memory 104 decrypts and expands the moving image data, and a graphic large scale integration (LSI) 105 transmits the decrypted and expanded moving images to an image memory 106. The transmitted moving images are converted into a format that can be displayed on a monitor 107 by the graphic LSI 105 (for example, converted from an YPbPr format into a digital red green blue (RGB) signal).
In the image processing apparatus, however, since an encryption/decryption key for moving images is incorporated into the image processing program in advance, the key can be extracted by analysis. Furthermore, the decrypted and expanded moving images can be read directly from the main memory 104 and the image memory 106. In an apparatus that adopts an open architecture, such as a personal computer, since an internal structure is well known, the above act can be easily conducted, compared with conventional audio and visual (AV) equipment.
On the other hand, all data in the image memory 106 including the moving images can be read from the processor 103. For this reason, the data in the image memory 106 (decrypted and expanded moving images) can be read in real time, copied, and distributed via the Internet without authorization during playback of the moving images.
A technique called “electronic watermark” leaves a proof that certain data are illegally copied in an ex-post manner in such illegal copies (for example, see Japanese Patent Application Laid-Open No. H10-234012).
An amount of information in moving images is considerably larger than that in still images, and a lot of information should be processed in a short time. In a system like national television system committee (NTSC), one image should be processed for every 1/30 second. That is to say, it should not take more than 1/30 second to put electronic watermarks into an individual image.
Some techniques to embed electronic watermarks into moving images under this limitation are suggested, roughly divided into two types including “visible watermark” and “invisible watermark”.
(1) Visible Watermark
This method continuously displays a certain logo on a part of a screen. NHK-BS and some communication satellite (CS) broadcasting adopt this method. A process for putting watermarks is easy and requires a short time, and the presence of watermarks is obvious for viewers.
(2) Invisible Watermark
This watermark is not accurately “invisible”, but is hard to be recognized by human eye. An original image is divided into frequency components by one-dimensional or two-dimensional Fourier transform, and data related to a copyright holder are inserted into one or plural specified high-frequency component(s).
In the visible watermarking method, however, a redundant component is continuously displayed on an original image, and this may cause discomfort to viewers. Some watermarks can be occasionally eliminated by less difficult means. For example, when a movie is broadcasted, a wide screen image is put on a television screen of 4:3, and thus black zones are formed on the top and the bottom of the main screen. A watermark displayed on such black zones can be easily eliminated.
In the invisible watermarking method, when algorithm for inserting an electronic watermark is once specified, the watermark can be eliminated easily by deleting whole frequency components corresponding to watermark inserting destination. In this case, since information on a portion of “hard to see” is deleted, image quality is not greatly deteriorated even when the watermark is eliminated.
For this reason, the invisible watermarking method is mainly applied to fields which are influenced easily by deterioration of an image. If image quality of a painting in art museum is deteriorated even a little, for example, the virtue of the painting is reduced greatly. For this reason, when such a painting is opened to the public via the Internet, the insertion of a watermark is effective. Meanwhile, unlike the painting, a moving image does not originally have very high image quality, and it is hardly considered that its value drops enormously due to the deterioration caused by eliminating the watermark.
Since the conventional electronic watermark can be eliminated comparatively with ease, image deterioration due to the elimination is small, and a source of an illegal copied product cannot be accurately specified from the watermark, even when the electronic watermark is embedded, the effect of protection from illegal copying can hardly be expected.